This invention relates to electric motors, and more particularly to fractional horsepower electric motors which are especially resistant to failures caused by moisture.
Fractional horsepower electric motors used in such applications as window air conditioning units, central air conditioning units, heat pumps, farm machines, swimming pool pumps, jet pumps and evaporative cooling units often operate in a high moisture environment. The source of the moisture can be rain, condensation, or even a water spray used to clean the motor. Generally, this moisture adversely affects the electrical insulation in the motor causing its dielectric strength and resistivity to degrade during prolonged exposure to moisture, to electrical stress, and to thermal cycling.
In particular, it has been noted that moisture is especially harmful to motor lead wire insulation, ground insulation, electrical connector insulation, electrical insulating varnish, and magnet wire insulation. Upon any of the above-noted insulation materials appreciably breaking down in a high moisture environment, the motor will, in many instances, develop an internal electrical short which will either cause the motor to fail to operate, to draw excessive current, or to pose an electrical shock hazard to personnel.
Of course, ventilated motors having open end shields or vents in their stator shells are particularly susceptible to attack by high humidity and by air borne liquid water droplets. In certain motor applications in high moisture environments, the use of totally enclosed motors are oftentimes specified in place of open ventilated motors because they have a superior service life. While totally enclosed motors do, in most instances, afford appreciably longer service life, totally enclosed motors are more expensive than ventilated motors of comparable output and, in certain high temperature environments, are difficult to cool. Of course, if totally enclosed motors are not adequately cooled, their efficiency will decrease appreciably.
There has been a long standing, industry-wide need for a conventional ventilated motor, which has a significantly increased service life in high humidity and in high moisture operating environments and which is not significantly more expensive than prior ventilated motors.